Ehm.. so.. GNOME wants our help now. But how did they behave when GNOME 3 was announced to not work without systemd? Or hey, anyone remember that discussion on a GNOME developers' mailing list, where they planned to take out theming support, because "it is going against the ubiquitous experience we envision GNOME 3 to be"? This smells fishy to me. (I said it more harshly, but realised that I went too far, sorry about…
GNOME 3 works on FreeBSD[1][2], you just don't get the robust and secure virtual terminal switching that only systemd's logind running on Linux can provide.
GTK+ 3 is now fully themeable with standard W3C CSS[3]. You may need to use Tweak Tool to change your theme, but is that really too much to ask for?
But please, don't let these facts stop you from cheering on large corporations as they trample all over open source projects.
[1] http://blogs.gnome.org/mclasen/2014/02/19/on-portability/ [2] http://blogs.gnome.org/desrt/2014/03/26/gnome-3-12-and-freeb... [3] https://developer.gnome.org/gtk3/stable/GtkCssProvider.html